The present application is based on and claims priority from Japanese Patent Application 2001-217686, filed Jul. 18, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a vehicle AC generator mounted in a vehicle, such as a passenger car or a truck.
2. Description of the Related Art
An AC generator is mounted in an automotive vehicle that is equipped with a gasoline engine or a diesel engine to generate electric power to be supplied to various electric loads and to be charged into a battery. The input torque of such an AC generator changes when some supply lines of the electric power are connected or interrupted or when engine angular acceleration changes. The input torque of the AC generator is usually calculated by an ECU (Electronic Control Unit) from duty ratio of current supplied to the field coil of the AC generator. However, it is difficult to accurately calculate the input torque only from the duty ratio because the input torque also changes with rotation conditions of the rotor of the AC generator.
The present invention has been made in view of the above problems.
It is a main object of the invention to provide a vehicle AC generator that can accurately calculate the input torque thereof.
According to a feature of the invention, a vehicle AC generator includes a pulley unit, a rotor, a field coil, a stator, a rate-of-change detecting unit and a signal unit.
The pulley unit has a one-way clutch that transmits driving torque of an engine in one-direction and interrupts the driving torque of the engine in the other direction. The rotor is connected to the pulley unit and has a plurality of magnetic poles. The field coil polarizes the magnetic poles when field current is supplied at a certain duty ratio. The stator has a stator winding that generates AC voltage when the rotor rotates and provide a rotating magnetic field. The rate-of-change detecting unit detects angular acceleration of the rotor when one-way clutch interrupts driving torque and the pulley rotates idle. The signal unit transmits a signal that indicates the rate-of-change of the rotation speed or angular acceleration to an outside device. The input torque of the vehicle AC generator is proportional to the rate-of-change of the rotation speed of the rotor. Therefore, the outside device that receives the signal indicating the angular acceleration can calculate the input torque accurately.
It is desirable that the angular acceleration detecting unit calculates a speed of the rotor from the AC voltage generated by the stator winding. Since the wave shape of the AC voltage generated in the stator winding synchronizes with the rotation of the rotor, the rotation speed of the rotor can be detected by measuring the AC voltage.
Preferably, the angular acceleration detecting unit judges whether the pulley idles or not by detecting speed reduction ratios of the rotor, whereby the idling rotation of the pulley can be detected without a special sensor.
The angular acceleration detecting unit may also judge whether the pulley idles or not by detecting increase in cycle period of the AC voltage generated by the stator winding.
The signal unit preferably includes a two-way signal transmitting unit for receiving control signals from an outside device and transmits signals indicating the rotation speed angular acceleration to the outside device.
The vehicle AC generator may include a torque calculation unit for calculating a product of a moment of inertia and the angular acceleration. In this case, the signal unit transmits a signal indicating the product of a moment of inertia and the angular acceleration to the outside unit.
The vehicle AC generator may includes means for detecting a duty ratio of the field current. In this case, the signal unit transmits a signal indicating the duty ratio instead of the signal indicating the angular acceleration when the duty ratio is larger than a predetermined value.
According to another feature of the invention, a vehicle AC generator includes a pulley unit, a rotor, a field coil, a stator, a cycle period detecting circuit and a signal unit.
The pulley unit has a one-way clutch that transmits one-way driving torque and interrupts the other driving torque. The rotor is connected to the pulley unit and has a plurality of magnetic poles. The field coil polarizes the magnetic poles when field current is supplied at a duty ratio. The stator has a stator winding for generating AC voltage when the rotor rotates to provide a rotating magnetic field. The cycle period detecting unit outputs a signal indicating a difference between a current cycle period of the AC voltage generated by the stator winding and a precedent cycle period generated a predetermined time before the current cycle period when the current cycle period is larger than the precedent cycle period. The signal unit transmits the signal indicating the difference to an outside device. Preferably, the signal unit includes a two-way signal transmitting unit for receiving control signals from an outside device and transmits signals indicating the difference to the outside device.
It is also preferable for the vehicle AC generator to include means for detecting a duty ratio of the field current. When the duty ratio is larger than a predetermined value, the pulley does not rotate idle. Accordingly, the signal unit transmits a signal indicating that the torque calculation is to be stopped to an outside control device.